<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        //检测是否是数字，包括整数，小数
        let str = prompt("请输入一个数字");
        let reg = /^(\-|\+)?\d+(\.\d+)?$/;
        if(reg.test(str)){
            alert("是一个数字");
        }else{
            alert("不是一个数字")
        }
    </script>
</body>
</html>